A more thorough explanation:

Theory of the case is a way of organizing facts and principles in a logical sequence to persuade a judge or jury to rule in favor of a litigant. It is the particular line of reasoning used by either party in a lawsuit to present their case in a way that produces a desired outcome.

For example, in a criminal trial, the prosecution's theory of the case might be that the defendant committed the crime with premeditation and intent, while the defense's theory of the case might be that the defendant acted in self-defense or was not present at the scene of the crime.

Another example could be in a civil lawsuit, where the plaintiff's theory of the case might be that the defendant breached a contract, while the defendant's theory of the case might be that the plaintiff did not fulfill their obligations under the contract.

The theory of the case is important because it helps the litigant to present their case in a clear and organized manner, and to persuade the decision-maker to rule in their favor.